Connecting rod for hermetic refrigerating compressor

ABSTRACT

The invention concerns a connecting rod for a hermetic refrigerating compressor, in which the connecting rod forms the mechanical connection between a crank and a piston. The purpose of the invention is to reduce wear in the crank bearing of the compressor with simple means. This is obtained by reducing compressive stresses in the connecting rod by making a cut-out in the connecting rod near the crank bearing. The cut-out causes deflection of compressive stresses, so that they are distributed over a larger share of the crank bearing surface. Also the outer shape of the connecting rod is adapted, so that also here the compressive stresses are distributed over a larger bearing surface. This reduces the wear on the crank bearing of the compressor and increases the life.

The invention concerns a connecting rod for a hermetic refrigeratingcompressor, in which a shaft is connected with a piston via a crank anda connecting rod, said piston making a forward and back stroke, theconnecting rod being connected to the crank by means of a first bearingand the to the piston by means of a connecting link, the connecting rodhaving means for preventing direct transfer of compressive stressbetween the common movement centre of the crank and the connecting rodand the common movement centre of the connecting rod and the piston.

U.S. Pat. No. 2,846,897 concerns a connecting rod for a combustionengine, in which the crank bearing comprises two halves assembled withbolts. The connecting rod consists of two longitudinally extendingflanges assembled with a central rib. On its transition to the crankbearing the central rib has an arched opening limited on both sides bythe longitudinally extending flanges.

DE 32 38 489 A1 also concerns a connecting rod for a combustion enginewith a crank bearing comprising a roller bearing, the problem to besolved being to secure the distribution of compressive stresses overseveral rollers. This problem is solved in that the connection betweenthe bearings of the connecting rod is formed by two flanges, which aremutually connected by a bridge, openings being made between the flangesand the bridge. Thus, it is obtained that compressive stresses are notdirectly transferred between the movement centres of the connecting rod,and that the stresses are distributed between several rollers. It isalso described that the bearing ring is resilient. However, a resilientbearing ring will yield to pressures, when it is not supported by theflanges. Thus, the forces will concentrate at the flanges, and thecompressive stresses between the flanges will be substantially reduced.The problem is solved in that with the two flanges the stresses can, inthe worst case, run through two rollers.

In both documents mentioned above, the compressive stresses run in theflanges, which are tangentially connected with the bearings. Thus, thereis hardly any direct transfer of compressive stresses between themovement centres, and the load on the bearings at the direct connectingline is very small. This gives an increased load of the bearings inother parts of the bearing circumference, where increased wear may causea reduction of the life. FIG. 1 shows a computer-simulated calculationof compressive stresses in a crank bearing, which is connected with theconnecting rod piston bearing by tangentially arranged flanges.

It is the purpose of the invention to realise an increased life of theconnecting rod for a hermetic refrigerating compressor using only simplemeans.

This task can be solved with a connecting rod as described in theintroduction, in that the connecting rod is provided with a cut-out,which cut-out is arranged at a distance to the bearing surface of thefirst bearing, the distance amounting to 15% to 30% of the diameter ofthe first bearing, the relation between the area of the first bearingopening and the area of the cut-out being 0.1% to 5%.

This gives an even distribution of the compressive stress over a largershare of the bearing surface, which results in reduced wear on theconnecting rod crank bearing. Only an adaptation of both placing andsize of the cut-out will give an optimum solution. If overcompensating,a drop may occur at the direct connecting line between the movementcentres of the connecting rod, and at the same time two new stressconcentrations giving wear problems may occur.

Advantageously, the invention can be made so that the largest transversemeasure of the cut-out is 5% to 15% of the inner diameter of the firstbearing of the connecting rod. This will give a relief of compressivestresses without causing the formation of new pressure peaks withdistance to the plane of symmetry.

Advantageously, the outer contour of the connecting rod around thecut-out is formed by a first concave line, which extends into a secondconvex line. Thus, the compressive stresses can run along the outside ofthe connecting rod without being deflected by sharp edges.

Advantageously, the material surrounding the cut-out facing the outercontour is thicker than the largest transverse measure of the cut-out.Thus, the compressive stresses can be distributed over a larger angle.

Advantageously, the cut-out is arranged at a distance from thecircumference of the first bearing, which distance is larger than thelargest transverse measure of the cut-out. Thus, compressive stressesare enabled to act directly under the bore.

Advantageously, the convex line of the outer contour forms an angle αwith the outer ring of the first bearing. Thus, production conditionsare considered, if the connecting rod has to be made as a sinteringworkpiece. The angle may also be necessary out of regard for the room ina hermetic compressor.

Advantageously, the cut-out is arranged on the connecting rod in aposition displaced to one of the sides in relation to the directconnecting line between the centres of the bearings. Thus, a reductionof the peak of the compressive stresses can be obtained. A friction inthe connecting rod bearings may cause a displacement of the compressivestresses from the symmetry line of the connecting rod in the directionof the edge of the connecting rod. To ensure a reduction of compressivestresses, the optimum arrangement and the shape of the cut-out can becalculated to be displaced in relation to the symmetry line. The outershape of the connecting rod can also be optimised in a way that thesides of the connecting rod deviate from each other.

In the following the invention is explained on the basis of drawings,showing:

FIG. 1 a computer calculated curve of the compressive stresses of thestate of the art

FIG. 2 a top-view of the connecting rod

FIG. 3 a section through the connecting rod

FIG. 4 a section of a connecting rod for a hermetic compressor from thestate of the art

FIG. 5 a section of a connecting rod with changed outer contour

FIG. 6 a section of a connecting rod with changed outer contour and athrough-going cut-out.

FIG. 7 curves of the radial load for the FIGS. 4, 5 and 6

FIG. 8 a top view of a connecting rod, the cut-out being shown as anellipse displaced from the symmetry line of the connecting rod

FIG. 9 a section through the connecting rod from FIG. 8.

FIG. 1 shows a computer-simulated graph of radial stresses, recordedacross a connecting rod as described in DE 32 38 489 A1. As theconnecting rod is symmetrical, the computer calculation has been madewith an increasing angle from the symmetry plane of the connecting rod.Thus, the curve only shows compressive stresses on one side of thecommon connecting line of the rotational points. FIG. 1 clearly showsthat the maximum compressive stresses are displaced by 40° in relationto the symmetry plane of the connecting rod. FIG. 1 shows a clearovercompensation, as the radial stress has been reduced to about 10% inareas around the symmetry plane, whereas the curve has a maximum at 40°,and as here the curve is symmetrical around 0°, it appears that two newpeaks of radial stress occur.

FIG. 2 shows a connecting rod 1 for a hermetic refrigerating compressor.The connecting rod has a first bearing 2, forming a bearing togetherwith the crank, the connecting rod and the crank having a commonmovement centre 4. The connecting rod also has a second bearing 3forming the connecting link to a piston (not shown), a common movementcentre 5 existing between the connecting link and the connecting rod.The connecting rod is shown with a throughgoing cut-out 6, here shown asa circular hole. The outer contours comprising a first concave line 7extending into a convex line 8 are also shown. Further, it is shown thatthe through-going cut-out 6 is arranged on the symmetry line 9 of theconnecting rod. On transition into the bearing 2, the convex line 8forms an angle α.

FIG. 3 shows a section through FIG. 2 along the symmetry plane 9. Itappears from FIG. 3 that the cut-out 6 is formed by a through-goingcircular hole.

FIG. 4 shows a section of a connecting rod for a hermetic refrigeratingcompressor according to the state of the art.

FIG. 5 shows a section similar to that in FIG. 4, the outer contours ofthe connecting rod having been corrected by the first concave line 7,which extends into a convex line 9, which ends with an angle a againstthe outer surface of the bearing.

FIG. 6 also shows a section of a connecting rod with the same outercontours as in FIG. 5, here with a through-going cut-out 6.

FIG. 7 shows the curves 10, 11 and 12, which have been computercalculated in the same way as the curve in FIG. 1. The curve 10corresponds to a connecting rod as shown in FIG. 4, whereas the curve 11corresponds to a connecting rod as shown in FIG. 5, and the curve 12corresponds to the connecting rod shown in FIG. 6.

Practical use of a connecting rod as shown in FIGS. 4 and 7, curve 10,will cause wear on the surface of the crank bearing 2 (FIG. 2), wherethe direct connecting line between the two movement centres crosses thebearing surface. In FIG. 7, the maximum radial stress is stated to havethe value 1. In curve 11, corresponding to FIG. 5, this value has beenreduced to about 0.93, and curve 12 shows a further reduction, namely to0.64 when using the connecting rod as shown in FIG. 6.

The height of the curve 12 has been reduced, and at the same time it hasbeen moved outwards, so that the radial load on the bearing isdistributed on a relatively larger share of the bearing circumference.Thus, the compressive stresses are distributed on a larger share of thebearing circumference, and wear on the bearing at the connecting linebetween the common movement centres of the connecting rod is avoided.

FIGS. 8 and 9 show an alternative embodiment with a cut-out 13 shown asan ellipse displaced from the symmetry line of the connecting rod.Frictional forces from the bearings of the connecting rod may act uponthe longitudinal compressive stresses of the connecting rod in a waythat they extend in a position displaced from the connecting line of themovement centres. Thus, an asymmetric arrangement of the cut-out may beexpedient.

An alternative embodiment with the same effect can be obtained with anon through-going cut-out, and particularly, if the connecting rod isproduced by means of sintering, it can be made with a non through-goingcut-out. Further, the desired effect can be obtained with cut-outs fromboth sides with a wall between the cut-outs. The invention can also bemade with several cut-outs from both sides.

What is claimed is:
 1. Connecting rod for a hermetic refrigeratingcompressor, in which a shaft is connected with a reciprocating pistonvia a crank and the connecting rod, the connecting rod comprising afirst bearing for connection to the crank, the first bearing having abearing surface and a predetermined diameter, the connecting rod furthercomprising a connecting link for connection to the piston, and anintermediate portion connecting the first bearing and the connectinglink, the connecting rod having means for preventing direct transfer ofcompressive stress between a common movement centre of the crank and theconnecting rod and a common movement centre of the connecting rod andthe piston, the connecting rod also having a cut-out in the intermediateportion, the intermediate portion having an entire solid structure withsubstantially uniform thickness, the cut-out being arranged at adistance from the bearing surface of the first bearing, the distanceamounting to 15-30% of the diameter of the first bearing, and thecut-out having an area and the first bearing opening having an area, theareas having a relation of 0.1-5%.
 2. Connecting rod according to claim1, in which the cut-out has a largest transverse measure of 5% to 15% ofthe diameter of the first bearing of the connecting rod.
 3. Connectingrod according to claim 1, in which the connecting rod has an outercontour around the cut-out formed by a first concave line which extendsinto a second convex line.
 4. Connecting rod according to claim 3, inwhich the material surrounding the cut-out facing the outer contour isthicker than the largest transverse measure of the cut-out. 5.Connecting rod according to claim 3, in which the convex line of theouter contour forms an angle α with the outer ring of the first bearing.6. Connecting rod according to claim 5, in which the angle a is between90 and 180 degrees.
 7. Connecting rod according to claim 1, in which thecut-out is arranged at a distance from the circumference of the firstbearing, which distance is larger than the largest transverse measure ofthe cut-out.
 8. Connecting rod according to claim 1, in which thecut-out is arranged on the connecting rod in a position displaced to oneof the sides in relation to a direct connecting line between the centreof the first bearing and the connecting link.